Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent) Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
The open-la500 core has USE_CACHE enabled. Writes to 0x1c400000 go to the write-back data cache and never reach the SRAM model before the testbench checks ExtRAM. Use the 0xA0000000 uncached segment (same pattern as fft_dma/main.c).
